Variable displacement engines are currently being developed to provide more efficient operation of automotive vehicles. Such a variable displacement engine is taught by Dolza in U.S. Pat. No. 2,875,742, and Barho et al. in U.S. Pat. No. 4,550,704.
One of the major problems encountered in variable displacement engines is that the spark plugs in the deactivated cylinders of the variable displacement engines tend to foul for various reasons. To prevent the spark plugs from fouling, Dolza teaches periodic alternating of the cylinder groups which are activated and deactivated at relatively frequent intervals while Barho et al. teaches alternating the cylinder groups which are activated based on the number of revolutions of the engine. Alternatively, Schechter, in U.S. Pat. No. 5,377,631, uses a skip cycle strategy in which a selected cylinder or cylinders are deactivated during a single cycle and a different cylinder or cylinders are deactivated in subsequent engine cycles.
As is recognized in the field of variable displacement engines, the fouling of the spark plugs in the deactivated cylinders is one of the major problems.
The prior art also teaches that the energizing of the spark plugs in the deactivated cylinders tends to enhance or increase the rate at which spark plugs will foul.